Electronic fluorescent illuminating lamp



' Ap 1958 ROGER FRANCOIS DESIRE NAVARRE 2,330,214

; ALIAS MALHERBE ELECTRONIC FLUORESCENT ILLUMINATING LAMP Filed Jan. 3,1955 2 Sheets-Sheet 1 ATTORNEYS p 1958 ROGER FRANCOIS DESIRE NAVARRE2,830,214 ALIAS MALHERBE ELECTRONIC FLUORESCENT ILLUMINATING LAMP 2Sheets-Sheet 2 Filed Jan. 5, 1955 m7 '4 V l/IIIIIIIIIIl/l/l INVE/V TORROGER FRANQO/S DES/RE NAVARREAUAS MALHERB/E 2,830,214 ELncrnoNrcFLUORESCENT ILLUMINATING LAMP Roger Frangois Dsir Navarre, aliasMalherbe, Paris, France, assignor, by mesne assignments, to Sebel S. An,Tangier, Morocco Application January 3, 1955, Serial No. 479,604

Claims priority, application France January 16, 1954 4 Claims. (Cl.313-109) anode, while a fluorescent coat is provided in the path of theelectrons emitted by the cathode, so that the kinetic energy acquired bysaid electrons under the action of the dilference in potential appliedbetween the anode and the cathode shall be transformed into luminousenergy at the moment of the impact of the electrons on the fluorescentcoat.

As disclosed in the above mentioned patent application, I have found,when executing such an illuminating lamp, that the spacing of the anodewith reference to the cathode requires, if it is desired to obtain asubstantial luminous intensity without employing prohibitive voltages,the use of means capable of neutralizing partly the space charge.

The principal means proposed for this purpose in the said patentapplication Serial No. 349,436 consist in inserting between the cathodeand the anode two grids one of which is brought to the potential of thecathode or to a potential that is slightly negative with reference tothe latter, while the other grid is brought to a potential that ispositive with reference to the cathode, the two grids havingsubstantially the same pitch and the bars or elements of the positivegrid being located in the electronic shadow of the grid which has a zeroor negative voltage with reference to the cathode.

The use of such a system of aligned grids applied thus for the firsttime to fluorescent electronic illuminating lamps of the type describedin the above mentioned patent application, was already known per se inthe execution of electronic tubes as used for usual electronicapplication purposes.

It has however been ascertained in accordance with the present inventionthat the execution of such a system requires solving a very particularproblem in the case of illuminating lamps, particularly due to the factthat, owing to the particular shape which must be given to the anode soas to provide for the desired efliciency of the emitted luminous flux,the anode-cathode distance is not uniform.

The present invention has more particularly for its object arrangementspermitting to obtain a practically uniform distribution of the electronsover the entire surface of the anode in spite of the particular shape ofthe latter.

Said arrangements will be better understood from the followingdescription, reference being made to the appended drawings given by wayof non-limitative examples, and in which:

Fig. 1 is an axial vertical cross-section of an electronic fluorescentilluminating lamp of the type described in the said patent applicationNo. 349,436;

Fig. 2 is a similar view of a modification of the lamp of applicationSerial No. 349,436;

United States Patent Fig. 3 is a diagram explaining the phenomena onwhich is based the present invention.

In the example illustrated in Fig. l, the chamber 1 of the lamp isdefined by a bulbof glass or the like transparent material, the shape ofwhich is similar to that of a mushroom and the socket of which isprovided with a fitting that is not illustrated and by which it may bemounted after the manner of the conventional'incandescent bulbs. 2designates an electron emitting cathode of the indirectly heated typeconstituted for instance by a nickel tube of any suitable cross-section,that is coated with emissive substances and is arranged substantiallyalong the axis of the bulb 1. The heating of said cathode is providedfor by a helically wound filament 9 of tungsten covered with alumina orthe like insulating material and extending inside the cathode tube 2.The cathode 2 and the filament 9 are fitted in the two superposed micawashers 10 and 11 carried at the corresponding ends of the cathode bythe socket in; said washers serve also as supports for the two grids 12and 13 surrounding the cathode 2 and which will be described withfurther detail hereinafter.

The inner wall of the portion of the bulb 1 nearest the socket iscovered by a metal layer 14 forming the anode and over which is applieda fluorescent coat 6. The wall of the part of the bulb that is opposedto the socket is, in the example illustrated, devoid of any coat andforms a transparent gate which provides a free passage for the luminousrays emitted by the coat 6 in the direction that is best suited for theutilization of the lamp.

The grids 12 and 13 are constituted for instance by helices of circularor rectangular cross-section that are secured to the mica washers 10 and11 by the longitudinal bars 15. The inner grid 12, located in theimmediate proximity of the cathode 2 is, in the present case,electrically connected with the latter. It may also be brought by anysuitable means to a negative voltage with reference to the cathode. Theouter grid 13 is connected electrically with the anode 14 or brought inany suitable manner to a positive potential with reference to thecathode. As already mentioned hereinabove, the convolutions of grid 13are arranged with reference to those of the grid 12 in a manner such asto lie in their electronic shadow.

In the modification illustrated in Fig. 2, the anode 14 and thefluorescent coat 6 are applied as in the'example of'Fig. 1 to theportion of the inner wall of the bulb 1 adjacent to the socket 1a, outthe cathode 2 and the grids 12 and 13' are constituted by flat elementsextending perpendicularly to the axis of the bulb 1, the heatingfilament 9 being positioned in parallelism with the plane of the latter.By reason of this arrangement, the infrared rays emitted by the cathode2 are directed for the major part towards that part of the wall of thebulb that is not coated with a fluorescent substance and they exertconsequently no light-extinguishing effect-on the coat 6.

Now, it is a well known fact that in an electronic device having alignedgrids successively spaced from the cathode, the electron beams startingfrom the cathode and passing respectively through the differentsuccessive grids are divergent and consequently cross one another so asto produce an area with a high electron density. This phenomenon isillustrated diagrammatically in the upper part of Fig. 3 in associationwith a chart in the lower part of Fig. 3 illustrating the spacialdistribution of the potentials, inside an electronic tube havingsuccessively positioned aligned grids, as a function of the location ofthe anode. In this representation of Fig. 3, K designates the cathode,and G1 and G2 designate the two aligned cylindrical grids of theembodiment of Fig. l surrounding the cathode, while A is the anode. Inthe chart in the lower part of Fig. 3, the distances between the anodeand the cathode are marked as abscissae while the voltages are marked asordinates. For sake of clarity, the voltage Va of the anode has beenassumed to be higher than the v taseVsZ el -the r d G2. but obviouslyother v u of the anodic voltage are also suitable.

Turning to Fig. 3, it is apparent that the above mentioned phenomenon ofhigh electron density due to beam crossover disturbs by no means thespacial distribution of the voltages between the grids G1 and G2 and theanode A for distances between anode and cathode such as those shown asDc and DI where there is no beam crossover. In contradistinction, whenthe anode is lo cated at distances from the cathode such as D2, D3, D4,etc., beyond distance Dc the space charge produced by the high electrondensity at the points where the electron beams cross one anotherdisturbs to a substantial extent the normal spacial distribution of thevoltages between G2 and A.

The distance Dc at which the electronic paths cross one another istermed the critical distance. Said distance depends, on one hand, on thegeometrical structure of the electrodes and, on the other hand, on thevoltages applied to the latter. in Fig. 3, the locus of points at thecritical distance is shown as a straight line, but it may be a curve,depending on conditions.

When the aligned grid systems are used in electronic tubes of the typeused for usual electronic application purposes wherein the anode-cathodedistance is uniform, it is of advantage to produce a space chargebetween the outer grid G2 and the anode so as to cut out any disturbancedue to an auxiliary emission of electrons. It is then unnecessary toprovide a suppressor grid. 7

It is thus apparent that in the case of tubes used for usual electronicsapplication purposes, it is of advantage for the anode to be alwayspositioned with reference to the cathode beyond the critical distanceDc. The action of the space charge thus produced on the secondaryelectrons which have a very reduced energy is considerable, and theaction of the space charge is on the contrary negligible on the primaryelectrons, except for very low anode voltages.

In the case of the fluorescent electronic illuminating lamp forming theobject of my said patent application Serial No. 349,436 (see inparticular Figs. 1 and 2 of the annexed drawings of this presentapplication), the anodecathode distance is not uniform, by reason of theshape to be given to the anode 14 so as to provide for the desiredefiiciency of the luminous flux. If it is desired to obtain a uniformdistribution of the beams of electrons over the entire surface of theanode 14, it is necessary for the locus of the points lying at thecritical distance to be very near the anode and to match the shape ofthe latter. This result may be achieved according to the presentinvention by giving a suitable shape to the cathode and to the alignedgrids and possibly by incorporating further electrodes of suitable shapeand at suitable voltages between the second or outer grid and the anode.

A simpler arrangement which forms also part of the present inventionconsists in positioning the point of the anode which is farthest fromthe'second or outer grid, within the critical distance. Thus there is nospace charge between the second grid and the anode.

In the case where the system comprising the cathode and the two alignedgrids does not lead to the production of a critical distance which islarge enough to allow satisfying the above-defined condition of locatingthe fartherest point of the anode, it is possible to associateadvantageously with said system additional electrodes having suitableshapes and maintained at suitable voltages so as to increasesufficiently said critical distance.

What I claim is:

1. An electronic fluorescent illuminating lamp comprising a transparentevacuated bulb, an electron-emitting cathode and an anode inside saidbulb, means for producing a flux of electrons between the cathode andthe anode, and a coat of fluorescent material carried inside the bulb inthe path of the electron flux and adapted to transform the kineticenergy of the electrons flowing between the cathode and the anode andimpinging on said coat into luminous energy, and two successively spacedgrids screening the cathode with reference to the anode, means forbiasing the first grid that is nearest to the cathode to a potentialthat is at the utmost equal to that of the cathode, and means forbiasing the second grid more remote from the cathode to a positivepotential with reference to the cathode, the two grids havingsubstantially the same pitch and the elementary parts of the secondpositively biased grid being located in the electronic shadow of theother grid, and the cathode and the two grids being soshaped andpositioned that the locus of the points located at the critical distanceof crossover of the two beams of electrons from the cathode passingrespectively through the said two grids is very near the anode andcorresponds substantially in shape to the latter.

2. An electronic fluorescent illuminating lamp comprising a transparentevacuated bulb, an electron-emitting cathode and an anode inside saidbulb, means for producing a flux of electrons between the cathode andthe anode, and a coat of fluorescent material carried inside the bulb inthe path of the electron flux and adapted to transform the kineticenergy of the electrons flowing between the cathode and the anode andimpinging on said coat into luminous energy, and two successively spacedgrids screening the cathode with reference to the anode, means forbiasing the first grid that is nearest to the cathode to a potentialthat is at the utmost equal to that of the cathode, and means forbiasing the second grid 7 more remote from the cathode to a positivepotential with reference to the cathode, the two grids havingsubstantially the same pitch and the elementary parts of the secondpositively biased grid being located in the electronic shadow of theother grid, and the cathode and the two grids and the anode being soshaped and positioned that the point of the anode which is the farthestfrom the second grid is located nearer the cathode than the locus ofpoints at the critical distance from the cathode of the crossover of thetwo beams of electrons from the cathode passing respectively through thesaid two grids.

3. An electronic fluorescent illuminating lamp according to claim 1, inwhich auxiliary electrodes suitably shaped and biased to bring the locusof the points located at the critical distance nearer to the anode areinserted between the said second grid and the anode.

4. An electronic fluorescent illuminating lamp accordingto claim 2, inwhich auxiliary electrodes value are inserted between the said secondgrid and the anode and areso shaped and positioned and biased as toremove the locus of points at said critical distance to be more remotefrom the cathode than the point of the anode which is farthest from thesecond grid.

References Cited in the file of this patent UNITED STATES PATENTS

